Julian Assange sought asylum at Ecuador's embassy in 2012 after a British judge ruled he should be extradited to Sweden to face allegations of sexual assault and rape (Photo: AFP)

A British minister on Tuesday branded Julian Assange a "miserable little worm" after the WikiLeaks founder, who is holed up in the Ecuadoran embassy in London, questioned the government's response to a nerve agent attack.

"It is of great regret that Julian Assange remains in the Ecuador embassy," Foreign Office minister Alan Duncan told MPs in the House of Commons in response to a question.

"It is of even deeper regret that even last night he was tweeting against Her Majesty's government for their conduct in replying to the attack in Salisbury.

"It's about time that this miserable little worm walked out of the embassy and gave himself up to British justice."

Assange sought political asylum at the embassy in 2012 after a British judge ruled he should be extradited to Sweden to face allegations of sexual assault and rape there.

He claims the accusations are politically motivated and feared it would lead to his extradition to the United States, which was enraged by WikiLeaks' publication of secret US military documents and diplomatic cables in 2010.

Sweden dropped its investigation last year, but the English warrant for his arrest for breaching bail conditions while awaiting extradition remains, meaning he would be detained if he stepped outside.

Assange has kept up his whistleblowing activities from inside the embassy and regularly tweets on international affairs.

On Monday night, he raised questions on Twitter about Britain's decision to blame Russia for the March 4 chemical weapons attack on a former double agent, Sergei Skripal, and its response -- echoed by more than 20 countries -- to expel Russian diplomats.